1. Field of the Invention
The present invention relates to a cylinder sleeve having an outer mantle surface that has a surface structure.
Cylinder sleeves for internal combustion engines are generally cast together with the crankcase. For this purpose, the cylinder sleeves are placed into a casting mold and the material of the crankcase is cast around them.
For the production of a crankcase for internal combustion engines, composed of a light metal material, generally ductile and high-strength aluminum alloys are used. The cylinder sleeves preferably consist of cast iron or a wear-resistant aluminum alloy. In this connection, however, no material-fit connection between the materials, i.e. no metallic bond between the material of the crankcase and the material of the cylinder sleeve, is formed. Therefore sufficient shape fit between the cylinder sleeves and the crankcase must be ensured.
2. The Prior Art
Cylinder sleeves are known from U.S. Pat. No. 3,165,983, which have ribs configured in star shape along their outer mantle surface, which ribs extend in the direction of the center axis of the cylinder sleeve and are introduced into the mantle surface by means of mechanical machining. It proves to be disadvantageous, in this connection, that gaps or interstices can form between the cylinder sleeve and the material of the crankcase, in the radial direction, as the result of tensile stress. As a result, local disruptions of the heat transfer between cylinder sleeve and crankcase can occur during engine operation. This results in a non-uniform temperature distribution in the cylinder, which in turn can lead to cylinder distortions, i.e. to deformation of the cylinders. Therefore the seal of the combustion chamber situated above the piston head, by means of the piston rings, is also impaired. As a known preventive measure, the piston rings are structured to have particularly high tangential contact forces. However, this leads to increased friction power and thus to increased fuel consumption during engine operation.
In order to counteract this problem, it is therefore desirable to produce a shape-fit connection between the cylinder sleeves and the crankcase, in such a manner that the connection does not come loose under tensile stress in the radial direction. It is known from EP 0 919 715 B1 to provide the mantle surface of cylinder sleeves with rib-shaped elevations, configured in the manner of a parallelogram, a trapezoid, or T shape in cross-section. Because of the clamping effect, a shape-fit connection between the cylinder sleeve and the crankcase is produced when casting takes place around such cylinder sleeves. It is proposed to produce such a surface structure by means of cutting work and/or plastic deformation. However, the production of such surface structures by means of forming methods is very complicated. Production by means of cutting work has the disadvantage that a suitable contour tool is required for this purpose, in order to achieve the desired undercuts. Furthermore, it has been shown that such tools wear out too fast, due to local overheating, particularly in the corner region.